package com.jxm.linear;

import java.nio.file.FileStore;

/**
 * @Author: jxm
 * @Description: 快慢指针解决单项链表是否有环问题
 * @Date: 2022/6/13 23:59
 * @Version: 1.0
 */
public class CircleListCheck {

    public static void main(String[] args) {
        Node<String> first = new Node<String>("aa", null);
        Node<String> second = new Node<String>("bb", null);
        Node<String> third = new Node<String>("cc", null);
        Node<String> fourth = new Node<String>("dd", null);
        Node<String> fifth = new Node<String>("ee", null);
        Node<String> six = new Node<String>("ff", null);
        Node<String> seven = new Node<String>("gg", null);
        //完成结点之间的指向
        first.next = second;
        second.next = third;
        third.next = fourth;
        fourth.next = fifth;
        fifth.next = six;
        six.next = seven;
        //产生环
//        seven.next = third;

        //判断链表是否有环
        boolean circle = isCircle(first);
        System.out.println("first链表中是否有环："+circle);
    }

    /**
     * 判断链表中是否有环
     * @param first  链表首结点
     * @return ture为有环，false为无环
     */
    public static boolean isCircle(Node<String> first) {
        //定义快慢两个指针
        Node<String> fast = first; //每次走两步
        Node<String> slow = first; //每次走一步

        //遍历链表，如果快慢指针指向同一个节点，那证明有环
        while (fast!=null && fast.next !=null){
            //变换快慢指针
            fast = fast.next.next;
            slow = slow.next;
            if(fast.equals(slow)){
                return true;
            }
        }

        return false;
    }

    //结点类
    private static class Node<T> {
        //存储数据
        T item;
        //下一个结点
        Node next;

        public Node(T item, Node next) {
            this.item = item; this.next = next;
        }
    }
}
